One way to combine various properties in one cleaning cloth consists in combining various types of fiber with each other for a given way to produce the fabric (as a woven or knitted fabric or as a nonwoven fabric, for example). Wovens or knits combining microfibers with thicker fibers thus exhibit good durability and also at least initially satisfactory performance characteristics. These fabrics, however, are disadvantageous in that they are more burdensome to produce than nonwoven fabrics. In addition, specifically fabrics produced by weft knitting with independently-movable needles are insufficiently retentive of microfibers. After about 400 industrial washing cycles (to DIN EN ISO 155797), nearly all the microfiber portions were found to have been removed. This is reflected in a distinct degradation of performance characteristics, such as handleability, skin sensorics, cleaning efficiency and/or water regimentation.
Nonwovens comprising microfibers are distinctly simpler to produce than wovens or knits. Nonwovens are structures formed from fibers finite in length (staple fibers), filaments (continuous-length fibers) or cut yarns of any type and origin that have been assembled into a web (a fiberweb) in some way and bonded together in some way. Microfiber nonwovens have in principle outstanding properties in the removal of soils and in pickup and release of liquids, particularly water. Existing microfiber nonwovens are disadvantageous, however, in that their durability, particularly to frequent washing in industrial washing cycles, is limited, as is reflected for example in holing occurring in the nonwovens after about 200 industrial washing cycles. When used in professional cleaning, with daily washing using disinfectant for example, these 200 washing cycles mean a service life of under a year.
In theory, raising the proportion of thicker fibers will improve nonwoven durability, since chemical and mechanical stability of single fibers/filaments increases with their thickness. However, this comes at the expense of performance characteristics.
Increasing the proportion of thin fibers leads as expected to improved performance characteristics, inter alia through improved water pickup due to the creation of a higher number of capillary interstices and through a softer hand due to reduced single fiber flexural stiffness. Sheet structures of this type, however, prove to be fragile when tear strength, pilling and particularly washability, especially washability at the boil, are compared with conventional textiles. Particularly performance characteristics ascribable to microfibers degrade significantly over time.
Namely, a PIE 16 nonwoven (70% PET 0.2 dtex, 30% PA6 0.1 dtex, split and hydroentangled) was found to suffer a distinct reduction in basis weight when subjected to a stress test of 400 washing cycles to DIN EN ISO 155797. Further analysis revealed that the polyamide fraction had declined from the original 30 down to 10 weight percent, whereas the PET fraction decreased less severely. This result was surprising in that bases, such as wash liquors, are known to attack PET, but not polyamide. A possible explanation for the result is that the comparatively fine polyamide filaments in the microfilament nonwoven are more likely to succumb to the chemical and mechanical stress in the wash and also to the high mechanical friction during tumble drying and to be transported away over time as broken fiber. This could also be due to the lower fiber thickness versus polyester.
The decrease in the proportion of PA6 after 500 washes in each case is illustrated in the table which follows. The residual polyamide content was determined by dissolving out with formic acid. It is the individual specimens which exhibit the variation in PA6 decrease.
TABLE 1Reduction in PA6 portion after 500 washes(60° C.) from originally 30% to:PETgivesPA6grosscorr; −0.073weighedcorr; −0.071PA6contentNo.gGggg%11.4751.4021.261.1890.21315.1920.6730.60.5930.5220.07813.0030.970.8970.8550.7840.11312.6041.5671.4941.361.2890.20513.7251.6051.5321.4421.3710.16110.5161.3011.2281.1731.1020.12610.26
These experiences suggest that the incorporation of twice as thick segments of PIE 8 for a given linear density of PIE 16 would improve the mechanical properties and robustness, and that the addition of half as thick segments coming from PIE 32, would lead to some restoration of sacrificed properties, such as moisture management and comfort.
A further way to combine downright contrary properties with one another in one sheetlike structure consists in forming a composite structure by combining two or more sheetlike structures. To this end, the individual sheetlike structures may be formed separately and then be combined with each other by means of known joining techniques, such as stitching, gluing, laminating.
Multicomponent spunbondeds having a linear density gradient are likewise known. EP 1 619 283 A1 describes multicomponent spunbondeds consisting of two or more polymers that form interfaces with each other and issue from one or more than one spinning apparatus having unitary spinneret die orifices and have been hydrodynamically attenuated, laid down in sheetlike form and—either as single plies or as multicomponent assembly—conjointly consolidated.
The problem addressed by the present invention is that of developing the known microfiber nonwovens further such that they offer good mechanical properties, in particular good sustained launderability coupled with good performance characteristics; good thermophysiological comfort; pleasant skin sensorics; pleasant appearance; good water management (absorption and water delivery, preferably at a uniform rate); and also good cleaning efficiency.